X-ray generator



Nov. 3o, 1943. z. J. ATLEE 2,335,253 i x-RAY GENERATOR Filed Nov. 25,1940 INVENTOR.

Patented Nov. 30, 1943 X-RAY GENERATOR Zed J. Atlee, Elmhurst, Ill.,assignor to General Electric X-Ray Corporation, Chicago, Ill., acorporation of New York Application November 25, 1940, Serial No.366,979

(Cl. ,Z50-148)l Claims.

My invention relates in general to anti-friction devices, and has moreparticular reference to bearings, especially bearings for service undervacuum conditions. The present application is a continuation in part ofmy co-pending application, Serial No. 284,273, filed July 13, 1939.

An important object of the invention is to provide means for processinga bearing in order, in a sense, to lubricate the same without using alubricant having a vapor pressure such as to cause evaporation of thelubricating medium and migration thereof from the bearing under thetemperature conditions to which the bearing is subjected when inoperation.

Another important object resides in providing a new method of insuringthat a bearing, operating under low pressure o-r vacuum conditions,shall retain its anti-friction qualities without resort to lubricationas presently applied in bearings, the invention having as a furtherimportant object the provision of a method of processing anti-frictiondevices of the character mentioned with a medium which has a vaporpressure sufficiently low so that it will not evaporate from the bearingand thus destroy the vacuum condition; a further object being toutilize, as a lubricating medium, an alloy of metals having vaporpressures of the order of -9 mms. of mercury at atmospheric pressure andnot to exceed 10-6 mm. of mercury at high temperatures of the order of200 centrigrade, whereby the lubricating medium may not migrate from atreated bearing operating under low pressure and high temperatureconditions.

Another important object resides in processing a bearing particularlyfor use in X-ray generators to support a rotating element of thegenerator for operation within a sealed evacuated enclosure in which theoperating temperature at the processed bearing may reach the order of200 centigrade and up.

Another important object resides in the provision of means for applyingthe lubricating medium to the bearing after the same has been sealedwithin the evacuated enclosure.

Another important object resides in applying a lubricating medium of thecharacter mentioned by flashing the same as a vapor upon the bearingsurfaces to be treated, and causing the vapor to condense upon saidsurfaces to form a lm of relatively soft material having lubricatingqualities but which will not migrate from the treated surfaces evenunder conditions of high temperature and low pressure through themechanical cohesion of the filmed material and its low vapor pressure.

Another important object resides in applying the material as a film onthe surfaces to be treated by providing a supply of said material inposition adjacent such surfaces, then evaporating or flashing thematerial, by heating the same, to produce vapor, and directing the vaportoward and upon the surfaces to be treated; a further object being toarrange the supply of material in a capsule or casing, preferably in theform of a hollow filamentary wire having a weakened Wall portion throughwhich the vaporized material may be expelled, the casing or capsulebeing mounted with its weakened wall facing toward the surfaces to betreated; a further object being to utilize an electrical current flowingin said lamentary wire capsule for the purpose of vaporizing thematerial.

Another important object is to provide means for delivering electricalcurrent for flashing the material to a supply of the material sealedwithin an evacuated chamber.

A further object is to provide an X-ray generator including a bearingenclosed in the sealed evacuated envelope of the generator, and inutilizing the stem on which the bearing is mounted as a circuit formingpart for the delivery of current to a supply of vaporizable materialwithin the envelope. These and numerous other important objects,advantages, and inherent functions of the invention will become apparentas the same is more fully understood from the following description,which, taken in connection with the accompanying drawing, discloses apreferred embodiment of the invention.

Referring to the drawing,

Figure 1 is a sectional view taken through an X-ray generator providedwith a rotating anode supported by a bearing structure of a type adaptedfor treatment in accordance with my present invention;

Figure 2 is an enlarged sectional view taken substantially along theline 2-2 in Figure l, illustrating one mode of applying my presentinvention;

Figure 3 is a sectional view taken substantially along the line 3-3 inFigure2; and

Figure 4 is lan enlarged sectional view taken substantially along theline 4 4 in Figure 3.

To illustrate my invention I have shown on lthe drawing an X-raygenerator Il comprising a rotating anode I3 supported within a sealedenvelope I1 on bearings l5, although it will be apparent, as thedescription proceeds, that my invention is not necessarily limited toX-ray generators or even necessarily to bearings for operation underconditions of high temperature and low pressure. Nevertheless, myinvention has great value in providing improved bearing means havingunusually ne operating characteristics at high temperature and lowpressure, and so I have chosen to demonstrate my invention as applied inX-ray generators, in the operation of which such excessive conditions ofhigh heat and low pressure are encountered.

The generator shown, of course, includes a cathode C of any usual orpreferred character, and the anode is supported by the bearing l5 on aspindle I9, which is shown mounted on and supported by the envelope Ilat one end thereof. As shown, the envelope has an extension 2 i, Withinwhich the anode I3 is snugly disposed for rotation, the envelope havinga reentrant sleevelike portion 23 forming an annular space 25 betweenthe envelope extension 2i and the reentrant portion 23.

The spindle I9 has an outwardly extending portion which is provided withmeans 29 forming an annular shoulder carrying an annular hanged member3| sealed thereon. The member 3| has a peripheral edge forming aglass-to-Inetal seal 33 with the inner end of the reentrant envelopeportion 23. This seal, through the member 3l, supports the spindle onthe envelope with a spindle portion 35 extendingr within the envelope,the anode bearings i5 being mounted on said inwardly extending spindleportion 35.

It should be understood that X-ray generators function to produce X-raysin response to the activation of the anode by electronic actionestablished by the operation of the cathode I3. This electronic actioncomprises the impingement of electrons emitted by the cathode upon atarget 31 forming a part of the anode, and such electronic impingernentresults in the generation of relatively large quantities of heat, whichis dissipated thence through the body of the anode I3, and also into theinterior of the casing Il. When in operation, the temperature of theX-ray generator and particularly of the anode may beof the order of500'centigrade.

In conditioning an X-ray generator for operation, the envelope l1 istreated to remove all gaseous and other impurities, the same beingaccomplished by evacuatingr the envelope as by means of a molecularexhaust pump while heating the elements of the generator to ahightemperature in order to drive out gases occluded in the envelope andall of the elements contained therein. The envelope finally is sealedafter all impurities have thus been eliminated.

During the operation of the X-ray generator as such, the anode I3 isdesirably rotated at high speed, in order to minimize the danger ofover-heating and burning the target itself, as a result of electronimpact. Considerable diiliculty has been encountered in providing meansfor supporting the anode for rotation during the life of the generator;under the excessively high temperature conditions and the low pressurenecessarily maintained within the envelope l1, since it is not feasibleto apply usual bearing lubrication because lubricants of the characterheretofore known will not remain in the bearings under tne lovvVpressure condition necessarily maintained in the envelope. but willinstantly evaporate and become dissipated within the envelope, thus notonly robbing the bearings of lubricant but also destroying the vacuum inthe tube and rendering the same inoperative. Consequently, it has notheretofore been considered feasible to lubricate bearings underconditions necessarily maintained in X-ray generators. Excessive bearingWear results, particularly at the high temperatures encountered in thegenerator, with the resultant development of anode vibration, whichrapidly renders the device unusable. Excessive bearing Wear also resultsin the production of minute wear products, which also impair theoperation of the generator as the same become dissipated from thebearings within the envelope.

My present invention relates to a method of lubricating bearings in amanner avoiding the aforesaid diiiiculties, particularly encountered inX-ray generators having rotating anodes; but the invention is by nomeans limited to such particular apparatus and, in fact, may be appliedto advantage in any bearing structure.

In practicing my invention, I select a suitable material adapted to beapplied as a vapor and to condense and form a lm upon the bearingsurfaces to be treated, the selected material desirably having severalqualities, including not only softness and ovvability, with low internalcoefficient of friction when in film-like form, but also suicientmechanical cohesion to cause the filmedmaterial tobe retained upon thetreated bearing surfaces, the property of wetting the bearing surfacesto be treated, lovv vapor pressure to prevent evaporation at thepressures and temperatures to which the treated bearing is to beexposed, and, unless the bearing is to be in operation in an oxygen-freeatmosphere, the lubricating material should not normally oxidize. Wherethe bearing is applied in an evacuated X- ray generator the problem ofoxidation of the filmed lubricating medium will not, of course, beencountered. However, if the treated bearing is for use in the ordinaryatmosphere, or elsewhere exposed to oxidation, the lubricating mediumshould be of a character normally resisting oxidation.

Barium, strontium, magnesium, and cobalt are metals adapted for use aslubricating media, in accordance with the teachings of my presentinvention; that combinations of these materials may be used; and, infact, in treating bearings for use in X-ray generators, I prefer toemploy barium, as a lubricating lrn applied upon the bearing surfaces.'I'he foregoing materials have vapor pressures of the order of l06 attemperatures of the order of 266 centigrade and are therefore welladapted for use as lubricants in bearings operating under low pressureconditions. Where operating pressures ale relatively higher, othermetals such as caesium and sodium are available in addition to thosespecified for excessively low pressure service.

The selected material is applied upon the bearing-surfaces, inaccordance with my present invention, by vaporizing the same anddirecting a stream of the vaporized material upon the bearing surfacesto be treated whereby thus to condense the vapor and form 'a thin iilincf the materia-l upon the surfaces to be treated. Vaporization anddelivery of theY material upon the surfaces may be accomplished in anysuitable or preferred manner. A supply of the material, for example, maybe positioned in a capsuie or container having an opening fancinfJr thesurfaces to be treated, and the material then heated in the capsule inany convenientmanner, as by the passage of an electrical current inorder to vaporize the material within the capsule and blowing theresulting vapor through the capsule opening and upon the surfaces to beprocessed. Alternately,

the material may be formed as a iilamentary wire,

in which the desired lubricating element is incorporated, and thenpassing an electrical current through the wire in order to expel thelubricating medium as a vapor upon the surfaces vto be treated. Suchwires as thoriated tungsten and alloys of silver and zinc may beutilized in this manner. Heating coils of tungsten wire in pocket shape,with a small quantity of the lubricating medium enclosed in the pocket,may similarly be used. As the tungsten wire is heated to the meltingpoint of the metal so enclosed, an alloy of the lubricating medium withthe tungsten wire may be formed on the surfaces of the wire, and thisalloy in turn may then be re-evaporated in order to produce a film ofthe lubricating medium upon the surfaces to be treated. This method issuitable for applying such materials as chromium, diiicultly obtainablein metallic state and possessing high melting point.

I prefer, however, in treating bearings for use in X-ray generators, toemploy a hollow filamentary wire W, preferably of iron or nickel,containing within the wire a quantity of the lubrieating material L,such as pure barium, the hollow wire being weakened by reducing its Wallthickness along one side of the wire, as indicated at S. By passing anelectrical current through the wire W, the material L maybe vaporizedtherein, the vapor products being blown out through the weakened wallsection S, and of course by supporting the wire with the surface Sfacing toward the bearing surfaces to be treated, the vaporized medium,may be directed directly upon such bearing surfaces.

As shown in the drawing, the anode I3-comprises a cylindrical bodyhaving an open end extending in the annular envelope space in posi'-tion to encircle the seal 33 at the inner end of the reentrant envelopeportion 23. The anode thus forms a shield for protecting the seal 33from deterioration through impingement of stray electrons thereon. Theopposite end of the anode body is enclosed, as at 39, and affords amounting for the target 31. Externally the cylindrical walls of theanode form a seat on which is secured the rotor 4I of an electricmoto-r, the stator 43 of which encircles the envelope extension 2I incooperative relationship with the rotor 4I whereby to drive the anodewithin the envelope when the stator 43 is excited from any suitablesource of electrical power externally of the envelope.

The spindle 35 extends within the cylindrical anode and carries thebearing means I5, said bearing means comprising in the illustratedembodiment a pair of roller bearings 44 and 46, in spaced-apart positionon the spindle portion 35. Each bearing comprises an outer race securedon the anode, and an inner race secured on the spindle portion 35,roller members of any suitable or convenient form, and illustrated asballs, be- A V ing conventionally retained between the inner and outerrace portions.

The anode I3 may, of course, be mounted on the bearing elements in anysuitable or preferred fashion, although I have shown the samein thedrawing clampingly secured on a cylindrical sleeve-like anode mounting.element 85, upon which the cylindrical anode member I3 is fastened, thebearings being enclosed within the hollow `bore 81 of the member 85. r

l The spindle portion 35 is formed with a shoulder 41 providing a seatfor the inner race of the bearing 44, the bearing being clamped in saidseat and held in position on the stem preferably by means of a nut 5Ithreaded on the stem. The stem 35 is also threaded to receive clampingnuts 53 and 55 between which is clampingly secured on the stem the innerrace of the bearing 46, and a he'atshield 51 may be provided for thebearing 46 and supported on the clamping nut 55 in position extendingbetween the target-carrying end of the anode, in which maximum heat isencountered during the operation of the device. This shield serves toprotect the bearing from heat radiated from said target-carryingportions of the anode, and tends to equalize the temperature under whichthe bearings 44 and 46 function.

The spindle I9 is provided with a longitudinally extending duct 59extending from the outwardly exposed end of the spindle to a point inthe spindle portion 35 intermediate the bearings 44 and 46, said duct 59opening laterally on the potrion 35 within the bore or channel 81 of theanode support element 85. The outer end of the duct 51 is enlarged, andhas sealed therein a sleeve 6 I, preferably comprising forty-two percentnickel steel, a material adapted to seal readily with glass.

A lead conductor 63 is arranged in the duct 59 with one end of saidconductor extending outwardly of the sleeve 6I, and the other endprojecting through the end of the duct which opens on the spindleportion 35. Suitable insulating means 65, such as a sleeve of magnesiumsilicate, or a plurality of glass beads embracing the conductor withinthe duct 59, is provided for insulating the conductor electrically fromthe stem I9 in which it is arranged, the outer end of the duct beingsealed preferably by means of a glass globule 61 applied within thesleeve 6I around the conductor 63.

Within the space 81 I mount suitable support means for a supply of thelubricating material L, and utilize the conductor 63 and the spindle I9as circuit forming means for electrically energizing the material L tovaporize the same within the channel 81, in order to process thebearings I5. In the illustrated embodiment this is accomplished byarranging a length of the filamentary tubular wire W on the stem portion35, said wire being arranged to form loops 69 in position opposite thebearings I5, with the weakened surfaces of the Wire portions formingsaid loops 69 facing toward the bearings. The loops 69 are electricallyinterconnected, preferably in series, in any suitable fashion by meansof an integral portion of the wire W extending between the loops 69. Oneof the loops is electrically connected as by soldering or welding thesame upon the spindle portion 35, the other loop being electricallyconnected with the end of the conductor 63 which is exposed within thechannel 81. If desired, the spindle 35 may be provided with insulatingmeans for supporting the lwire W rigidly in position, althoughordinarily additional support is not required since the wire itself hassuicient rigidity to maintain itself in assembled position, at leastuntil after the material L has been flashed in processing the bearmg.

Itwill be seen from the foregoing that by connecting a suitable sourceof electrical potential between the outwardly exposed end of theconductor 63 and the spindle I9, an electrical heatingcurrent may becaused to flow through the 'wire W in order to 'raise the temperature'of the wire `toa point at which the material vL vaporizes, in orderthus, as heretofore described, to cause the expulsion of Vapor throughthe weakened wall Sat the loops 69 vand thence upon the bearings. i

VThe bearings preferably are thus processed kfor the application of a lmof the lubricating medium L thereon, after assembly in the envelope iland after the envelope has been evacuated, as heretofore described, sothat flashing of the material L is accomplished substantially in vacuoand after the envelope Il has been completely sealed. The flashproducts, however, will not escape to any detectable extent from thehollow anode. The vaporized products, however, impinging upon the facingsurfaces of ther bearings, which preferably are rotated during theflashing of the material L, immediately condense upon the surfaces toform a film thereon, the inner face vof the lm wetting the surfacematerial of the bearing and forming an alloy therewith which holds thelm in place. The rotation of the bearings causes substantially all ofthe surfaces thereof required to be treated to receive the coated filmof the lubrieating material; and since the flash products are confinedsubstantially within the chamber 3l, no migration of such productsoutwardly of the bearings and the hollow anode is detectable, and thevacuum condition Within the envelope is not in any way impaired as aresult of the dashing operation.

In order to seal and protect the exposed end of the conductor 53, theouter end of the stem I9 may be threaded, as shown at 7l, to receive acover cap 73, the outer end of which may be threaded as shown, orotherwise finished as desired, said cap being preferably threaded forthe reception of heat dissipating means thereon by means of which heatdeveloped at the anode may, in part, be dissipated from the generator byconduction through the anode support sleeve 85, -the bearings l5, andthe spindle outwardly of the envelope il'.

The flashing of the material L from theV wire W may be controlled sothat the lubricating medium I.- may be repeatedly fiashed on the bearingsurfaces. This may be accomplished in any suitable manner, for example,by controlling the amount of heating current and the time of ow throughthe wire W. In this manner, the lubrication of the bearings can berenewed from time to time in a very simple manner.

It has been found that the best results are obtained where there isapparently the formation of an alloy. This may be accomplished byvaporizing on the working surface of the bearing in succession two ormore thin fllms of a metallic lubricating medium, or by forming thebearing itself of a type of material which forms an allof,1 with themetallic vapor that is flashed on the bearing surface. In general, thislatter method is preferred, because the lubricating alloy is an integralpart of the working surface of the bearing. It will be understood thatthe working surface of the bearing may be such that the rst vapor-izedthin metallic coating applied will alloy therewith and the secondvaporized thin metallic coating will alloy with the first. The life ofthe lubrication is not as long if neither of the metallic coatings hasan alloying action with the metal or metals from which the workingsurface of the bearing is made.

Excellent results have been obtained when the Working surface of thebearing has been formed of a high speed tungsten-cobalt steel, such asCircle `C (Firth Sterling Company), this alloy comprising about 18%tungsten, about 9% cobalt, about 4.5% chromium, about 1.75% vanadium,about 1% molybdenum, and 0.77% carbon, the remainder being substantiallyall iron. Among the metals which have been applied as a vapor to thistype of bearing are the following: Barium, zinc, magnesium, strontium,calcium, silver, aluminum, gold, copper, iron, nickel, cobalt, platinum,and chromium. While some of these materials yielded results similar tothose obtained with barium, none gave any better results. It will berecognized that there is a possibility of two or more different alloysbeing formed where the bearing surface is formed from an alloy. Forexample, in employing a bearing material of the type just mentioned, itis possible that the lubricating alloy formed may be a barium-cobaltlayer, and since chromium is also present, there may also be abarium-chromium layer.

The lubricating action has also been obtained by vaporizing barium onto18% chromium, 8% nickel stainless steel bearing surfaces. In one seriesof tests, a layer of cobalt vaporized on S. A. E. 52-100 steel providedrelatively slight lubrication and vaporized barium alone provided veryslight lubrication, but just as soon as a barium layer was added on topof the cobalt, excellent lubrication developed. This proves very clearlythat at least one lubricating film is a combination of cobalt andbarium.

vI have found that bearings treated in accordance with the teachings ofmy present invention are able to operate substantiallywithout wear andwithout conventional lubrication throughout extended service periods,under eX- cessive low pressure and high heat conditions. When used inX-ray generators, bearings Drocessed in accordance with my presentinvention have an extended service life, usually ontlasting the normallife of the generator itself.

It is thought that the invention and its numerous attendant advantageswill be fully understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction, andarrangement of the several parts without departing from the spirit andscope of the invention, nor sacrificing its attendant advantages, theforms herein disclosed being merely for the purpose of demonstrating theinvention.

The invention is lhereby claimed as follows:

1. An X-ray generator comprising an evacuated casing, an electrode,bearing means having working surfaces turnably supporting the electrodewithin said casing, and a thin alloy lm coated on said working surfacesto lubricate said bearing means, said alloy lm including a metal oftheclassv consisting of barium, magnesium and strontium, alloyed with thematerial of said working surfaces, and cobalt.

2. An X-ray generator comprising a'n evacuated cas'ing, an electrode,bearing means having working surfaces turnably supporting the electrodewithin said casing, and a thin alloy film coated on said workingsurfaces to lubricate said bearing means, said alloy lm including ametal of the `class consisting of barium, magnesium and strontium,alloyed with the material of said workin'g surfaces, and including analloy including cobalt as an alloy constituent thereof.

3.A'n X-ray generator' comprising an evacuated casing, an electrode, andbearing means turnably supporting said electrode within said casing,said bearing means having Working surfaces comprising an alloy includingbarium and cobalt as alloy constitutents thereon.

4. An X-ray generator comprising an evacuated casing, an electrode, andbearing means turnably supporting said electrode Within said casing,said bearing means having Working surfaces comprising an alloycontaining cobalt as an alloy constituent and having a thin film ofmetallic barium condensed thereon and alloyed with the cobaltconstituent of said working surfaces.

5. An X-ray generator comprising an evacuated casing, an electrode,bearing means having Working surfaces turnabiy supporting the electrodewithin said casing and comprising a1- loy steel including cobalt as analloy constituent of the steel, and a thin alloy film coated on saidWorking surfaces to lubricate said bearing means, said alloy filmincluding a metal of the class consisting of barium, magnesium andstrontium, alloyed with the material of said working surfaces,

ZED J. ATLEE.

